With the increase in communication demand, there has been used an optical transport network (OTN) technique which facilitates large-capacity data transmission (see, e.g., WO 2014/013602). The OTN technique is defined in, for example, the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) Recommendation G.709.
An OTN transmission system facilitates large-capacity transmission since a plurality of client signals is transmitted in a state of being accommodated in a signal of a format of an optical channel transport unit (OTU) frame (hereinafter referred to as an “OTU” signal). Examples of the client signals may include a synchronous digital hierarchy (SDH) frame, a synchronous optical network (SONET) frame, an Ethernet® frame and the like. In addition, a plurality of types of OTU frames (e.g., OTU1, OTU4, etc.) is defined in the ITU-T Recommendation G.709 depending on a transmission rate.
A signal processing circuit for the OTU signal is divided into a plurality of stages by, for example, a field programmable gate array (FPGA). A plurality of signal processing circuits subjects the OTU signal to a frame synchronization process (see, e.g., Japanese Laid-Open Patent Publication No. 1-278139), and then, subjects the OTU signal to different types of processes in a sequential manner.
For example, for a FPGA of a 28 (nm) or 20 (nm) process, the OTU signal is processed after being parallel-converted by, for example, a serializer/deserializer (SERDES) circuit so that each signal processing circuit can sufficiently process the OTU signal even at a clock speed of about 200 (MHz). For example, for OTU4, the OTU signal is converted into 640 parallel data.
Related technologies are disclosed in, for example, WO 2014/013602 and Japanese Laid-Open Patent Publication No. 1-278139.